The specific objectives of this project are: (1) determination of the level(s) of control of aminoacyl-tRNA synthetase formation; (2) a comprehensive and full determination of the effector molecule or molecular complex that serves to generate a positive or negative signal for synthetase formation; and (3) a detailed analysis of the physiological significance of variations in the levels of the synthetases relative to amino acid biosynthesis and macromolecular (primarily stable RNA and proteins) synthesis in general in both Escherichia coli and Salmonella typhimurium.